1. Field of Invention
The present invention relates to delivery devices for the delivery of fluids into persons in need thereof. In particular this invention is related to devices, for the delivery of fluid medications into patients. These devices are multi-dose delivery devices, where a pre-selected quantity of fluids can be delivered into patients. The devices of the present invention have the overall shape and appearance of a pen, and hence have been described as “fluid delivery pens”.
2. Background of the Invention
Delivery of fluids to persons in need thereof, is often necessary, in fixed doses, and/or at regular intervals. Patients, for instance, are often in need of regular doses of specific medications. For instance, diabetics require several doses of insulin injections during the course of the day. The required insulin regimen varies from patient to patient and depends on the type of insulin to be injected (slow, medium, fast acting, or specific combinations of these), the lifestyle of the patient, the circumstances, patient's actual medical condition etc. Hence diabetics often need to self-administer their medication, at the appropriate time, in the appropriate doses, and in places other then a health center, such as their homes, offices, restaurants etc. Thus a delivery device for use in such circumstances must be easy, convenient, as well as non-embarrassing to use, and convenient to carry around in public. Fluid delivery pens have been developed to enable such self-administration of devices.
Typically a fluid delivery pen comprises a cartridge holder into which a cartridge of fluids, such as a liquid medication, is loaded. The cartridge holder usually has an elongated tubular design, whose distal end is adapted to carry a needle assembly, such that the proximal tip of the needle, carried by the needle assembly, is in direct contact with the fluid inside the cartridge. The proximal end of the cartridge is generally closed with a plunger, whose inner surface is in contact with the fluid. The outer surface of the plunger is in turn connected to a piston rod. A measured movement of the plunger-piston rod in the distal direction results in the delivery of a measured dose of the fluid. The delivery device is calibrated such that the dose delivered is directly related to the movement of the plunger in the distal direction. In addition the delivery device comprises a dose setting means for setting the dose of the fluid to be dispensed, and a driving means for pushing the plunger through a distance determined by the dose setting means. The piston rod, dose setting means and driving means are enclosed, partly or wholly, in a housing. The distal portion of the delivery device, that carries the needle assembly, is enclosed by a cap.
The shape of the device is similar to a pen of suitable weight and length that can be carried conveniently in the pocket. Such fluid delivery devices are used by first loading the cartridge holder with the fluid containing cartridge, mounting the needle assembly, setting the appropriate dose and injecting the fluid. Such devices are described as “reusable”, when an empty cartridge is replaced by a fresh one, as opposed to “disposable” ones, that come supplied with the cartridge, and is discarded once the cartridge is empty.
There can be several variations to the above general design.
For instance, the needle assemble may be reusable or fixed, the dose setting device and driving means may differ in different types of devices, the dispenser may have a feature which could allow the piston rod to travel only in one direction. In addition, the devices may differ in the nature of the scales used to set dosages, and the convenience in using them.
While the devices presently available have served the general purpose as devices for the convenient self-administration of fluids, such as drugs, there is, nevertheless, ample room for improvement in the design of such delivery devices.
For instance, it would be desirable if the mechanism could accommodate both reusable and disposable feature. It would also be desirable if the working mechanism of the device is designed in a configuration that is adaptable to a range of body shapes and styles.
Additionally, it would be desirable if the device can be assembled from as few individual components as possible, and that the components are designed for fast and efficient assembly, either manual or automated.
Another desirable feature would be a device whose parts are made of plastic that can be recycled. It would be further desirable if the device is designed so that setting and injecting doses are easier for the elderly and physically challenged. This could be accomplished, for instance, by incorporating mechanisms that produce tactile and auditory “clicks” while the dose is being set—every “click” indicating a change in a unit dose setting.
Also it would be desirable to incorporate a magnifying lens to magnify the numerals on the dose dial to improve readability for the visually challenged.
It would also be desirable if the parts of the device can be designed in sub-assemblies, since this enables functional areas of the pen to be checked and tested separately, and in greater detail, before the pen is fully assembled.
Another desirable feature would be a device that has a direct mechanical drive between the person applying the injection force and the piston rod being driven forward to inject the medicament. This ensures the person is aware of any problems in the dose delivery. Mechanisms which, for instance, use a spring force to eject the dose, such as those described in U.S. patent U.S. Pat. No. 5,104,380, can occasionally deliver an incomplete dose if the force required to push the cartridge is greater then would normally be the case. It is also desirable that where a set dose can't be fully delivered, because the cartridge becomes empty, the device can indicate to the patient how much of the dose has been delivered.
It would also desirable if the delivery mechanism offers a mechanical advantage to the user to reduce the force that must be applied by the user during injection. In U.S. Pat. No. 4,973,318 for instance, the user has to depress the application knob with the same force and over the same distance as required to move the cartridge. For the smooth running of the piston drive mechanism, it is important that dirt and dust are not allowed to enter the mechanism. Many delivery mechanisms in the prior art, such as those described in U.S. patents U.S. Pat. Nos. 6,235,004, 6,004,297, 5,611,783, 6,454,746, 5,279,586 etc., have an externally exposed threaded piston rod which, in a reusable device, could be vulnerable to picking up dirt and dust thereby hindering the working mechanism. It would hence be desirable if the thread drive mechanism is enclosed and thus protected from dirt and dust when the cartridge housing is removed.
Also in reusable devices it would be desirable that the piston rod is of strong design to avoid damage when changing cartridges or resetting the mechanism. Such resetting often involves the use of a non-locking thread, and as a consequence a given diameter of the thread cannot be exceeded for any particular thread pitch. This results in many externally threaded piston rods in the prior art being of relatively small diameter, and therefore vulnerable to damage or deformation. Examples of patents with outer threaded piston rods include U.S. Pat. Nos. 6,235,004, 6,004,297, 5,611,783, 6,454,746 and 5,279,586. A piston rod that has an internal non-locking thread can be substantially larger in diameter and will have a structurally efficient hollow cross section making it substantially stronger then an equivalent externally threaded rod.
The present invention describes a fluid delivery device incorporating all the features described above. The description outlined below is for illustrative purposes and is not intended to limit scope of the invention either in its design or its application.